World-wide, substantial amounts of land have become metal contaminated as a result of industrial, waste disposal and other activities. Examples of such contaminants include: mercury, cadmium, barium, chromium, manganese and lead, radionuclides such as actinides and fission products. Such contaminants can pose a significant threat to ground water and therefore drinking water supplies and in many cases either limit, or prevent land re-use. Additionally, as a result of recent legislation in the United States of America and likely similar legislation within the European Community and elsewhere, waste producers are becoming increasingly liable to prosecution and to meet the costs of recovery and clean up if they do not act responsibly towards their wastes. Consequently there is a growing need for technologies which can help solve the problems caused by contaminated land.
To date, a number of techniques have been developed to remediate contaminated land. Examples include: soil stabilization, electromigration, vitrification, volatilization, incineration, soil washing, pump and treat systems, land farming, slurry phase bioremediation, etc. Many of these known techniques possess several limitations including:
a) Lack of a permanent solution to the problem, e.g. transferral of the material to a toxic landfill, or entrapment within matrixes possessing a limited life; PA1 b) Unsuitability to treat a wide range of contaminants, e.g. metal contaminated land in the case of currently used biological processes; PA1 c) The generation of high volume, or difficult to control secondary wastes, e.g. soil stabilization and incineration; PA1 d) Lack of selectivity of in-situ or ex-situ options as appropriate to a particular site, e.g. as in the case of incineration and soil washing; PA1 e) High costs, e.g. incineration, vitrification and pump and treat systems; PA1 f) Limited ability to re-use contaminants, e.g. soil stabilization systems when applied to metals. PA1 i) actinides or their radioactive decay products or compounds thereof; PA1 ii) fission products; PA1 iii) heavy metals or compounds thereof. PA1 a) direct attack of metal sulfides; PA1 b) by electrochemical processes (galvanic conversion), resulting from contact between two dissimilar metal species immersed in a suitable electrolyte, e.g. sulfuric acid; or PA1 c) by the oxidative effect of ferric sulfate. PA1 (a) sludge containing precipitated metal sulfides and biomass; PA1 (b) aqueous hydrogen sulfide and soluble metal sulfides together with some biomass components; PA1 (c) gaseous hydrogen sulfide. PA1 (a) direct oxidation to sulfuric acid and/or sulfates; PA1 (b) oxidation to elemental sulfur, which can if appropriate then be added to, e.g. spread on, the contaminated soil to produce sulfuric acid.
The present invention seeks to address these problems by enabling biological systems to remediate metal contaminated land non-specifically.